1. Field of the Invention
This invention relates to a lathe programming apparatus which automatically produces a numerical control (NC) tape for machining a workpiece to a predetermined shape based on a conversational machining program by means of a computer-controlled NC lathe or the like.
2. Description or Related Art
In order to fabricate a workpiece having a complicated and intricate structure when subjecting the workpiece to machining using a cutting tool, drill, milling machine or the like, positional coordinates are decided by utilizing a keyboard and display, for example, to prepare machining data for numerical control (NC). A machine tool is numerically controlled by an NC tape prepared by an NC unit based on a machining tool, thereby subjecting the workpiece to desired machining.
In order to compute a tool path, a coordinate system conforming to the method in which dimensions are written on a design drawing is selected using a graphic display. Data such as the shape of the workpiece blank, the dimensions thereof and the position of a base line are entered. While observing the display on which the coordinate axes and blank shape appear, the operator presses shape symbol keys on a keyboard to input the machining shape and, as machining position data, the dimensions necessary for each portion of the shape.
In machining by lathe, there are instances where a machining process referred to as "C-axis machining" accompanies outer-diameter machining and inner-diameter machining. In C-axis machining, the usual practice is to change the tool in use at the end of outer-diameter machining and designate a machining position which intersects the preceding tool path. When machining position data for a portion to be subjected to such additional machining are input, these data are entered overlapping the data used in computing the tool path for the preceding machining. This is inconvenient in that the programming operation requires time. The inconvenience is not limited to C-axis machining. In particular, reading the required numerical value data from a design drawing which includes a plurality of portions for additional machining is a source of input errors when performed by a beginner. Accordingly, an improvement in the operability of the apparatus is desired.